http://gcc.gnu.org/bugzilla/show_bug.cgi?id=56875
Bug #: 56875
Summary: vax target miscompiles short negative constants for
64bit values
Classification: Unclassified
Product: gcc
Version: unknown
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: target
AssignedTo: unassig...@gcc.gnu.org
ReportedBy: mar...@netbsd.org
Created attachment 29823
--> http://gcc.gnu.org/bugzilla/attachment.cgi?id=29823
Use the D format specifie for ashqs second arg
The documentation for VAX operand formatting codes says:
D 64-bit immediate operand
and:
/* The purpose of D is to get around a quirk or bug in vax assembler
whereby -1 in a 64-bit immediate operand means 0x00000000ffffffff,
which is not a 64-bit minus one. */
However, the ashq instruction patters do not use this properly.
This small test program triggers it:
#include <stdio.h>
#include <inttypes.h>
int main(int argc, char **argv)
{
size_t i;
uint64_t v, nv;
for (i = 0; i < 16; i++) {
v = ~(uint64_t)0 << i;
nv = ~v;
printf("%zu: mask %08llx not %08llx\n", i, v, nv);
}
return 0;
}
The relevant line from assembly:
ashq %r6,$-1,%r2
which is misinterpreted by the assembler, so dissasembly is:
10637: 79 56 8f ff ashq r6,$0x00000000ffffffff,r2
1063b: ff ff ff 00
1063f: 00 00 00 52
The attached patch fixes it.
